Many prior art methods for quantitatively measuring cell identity, such as immunocytochemistry (antibodies to marker proteins), gene arrays, and PCR (tests for mRNA characteristic of stem cells) are destructive tests that do not allow cells to continue growing.
Fluorescent methods for measuring cell identity can be non-destructive, but may be invasive or require perturbation of the cells. For example, flow cytometry requires the labeling of specific cell surface markers and single cell suspension in liquid culture. These disruptions can be very harsh and can result in the death of a majority of cells. Transgenic fluorescent techniques using fluorescent proteins can be performed in cells that remain alive but still require genetic perturbation of the organism. These and other approaches are appropriate when invasive markers of cell identity or quality are used to evaluate samples representative of larger populations of similar cells, but cannot be used to evaluate an entire population of cells that are needed for live cell growth and expansion. These techniques require measurements on a few cells thought to be representative of a larger population of cells and are subject to statistical error in heterogeneous samples.
Alternative non-destructive methods include, for example, visual inspections of the cells in a microscope. For example, stem cell lines must be monitored daily to determine which of the cultured colonies are sufficient for use in experiments and therapies. These human-based methods are non-quantitative and prone to the biases and errors of the human eye. They are also time consuming and labor intensive, and are therefore impractical in the case of high volume cell culture. Another limitation of inspector based methods is the inability to produce records of cell culture that can be compared from sample to sample over time, to promote reproducible biological products suitable for medical therapy or large scale biological experiments.
Thus, disadvantages of prior art methods (visual inspection) include that some are manual, time consuming and inconsistent, while others are invasive, destructive, or both.